It has long been clear that none of the existing models of the respiratory control system adequately explain the precise relationship between the increase of ventilation and that of metabolism in exercise. The proposed studies are based on the hypothesis that neural input to the respiratory control system and neural mechanisms within the system are more important than traditionally believed. In order to study this, it is proposed to use neural output to represent ventilation, thereby allowing an "open loop" control system which avoids the negative chemical feedback associated with changes in ventilation. The first step has been to develop methods of handling phrenic nerve output so that an accurate and repeatable neural equivalent of tidal volume, a neural representative of central respiratory drive, is obtained. The phrenic output is then used in paralyzed ventilated animals to study the effect of various neural inputs on central respiratory drive. Especially to be studied are (1) the effect of timing of brief stimuli from a variety of sources on respiratory drive and (2) the apparent property of the central mechanism to sustain ventilation for a significant period after removal of a peripheral forcing stimulus. These findings should be useful in the better understanding of control mechanisms during respiration at both rest and exercise.